Proceed to Payment Options button, no longer working

We have a registration that is no longer working and cannot figure it out. The form has been used for about a year already and it worked fine until 10/10. Already checked if there were any updates (plugins or themes) on that date and have removed 2 plugins that may conflict with EE. Still, the button is not working.

Below is the link to the form, you can access it, fill in the information, but cannot go to payment, the error says:

This registration step could not be completed. Please refresh the page and try again.

Refreshing does nothing. Any insights into what else to look for? I am new to EE.